Reverse a string without affecting special characters
Last Updated :
18 Jan, 2023
Given a string, that contains a special character together with alphabets ('a' to 'z' and 'A' to 'Z'), reverse the string in a way that special characters are not affected.
Examples:
Input: str = "a,b$c"
Output: str = "c,b$a"
Explanation: Note that $ and , are not moved anywhere. Only subsequence "abc" is reversed
Input: str = "Ab,c,de!$"
Output: str = "ed,c,bA!$"
Simple Solution:
- Create a temporary character array say temp[].
- Copy alphabetic characters from the given array to temp[].
- Reverse temp[] using standard string reversal algorithm.
- Now traverse input string and temp in a single loop. Wherever there is an alphabetic character is input string, replace it with the current character of temp[].
Below is the implementation of above approach:
C++
// C++ program to reverse string without
// affecting it's special character
#include <bits/stdc++.h>
using namespace std;
void reverse(string s)
{
// creating character array of size
// equal to length of string
char temp[s.length()];
int x = 0;
for (int i = 0; i < s.length(); i++) {
if (s[i] >= 'a' && s[i] <= 'z'
|| s[i] >= 'A' && s[i] <= 'Z') {
// storing elements in array
temp[x] = s[i];
x++;
}
}
// reversing the character array
reverse(temp, temp + x);
x = 0;
for (int i = 0; i < s.length(); i++) {
if (s[i] >= 'a' && s[i] <= 'z'
|| s[i] >= 'A' && s[i] <= 'Z') {
// updating the original string
s[i] = temp[x];
x++;
}
}
cout << "reversed string is: " << s;
}
// driver code
int main()
{
string s = "Ab,c,de!$";
// function call
reverse(s);
return 0;
}
// this code is contributed by Machhaliya Muhammad
// Java code to illustrate how to reverse a string without
// affecting special characters.
import java.util.*;
class GFG {
public static void rev(char s[], int l, int r)
{
for (int i = l; i < r / 2; i++) {
char temp = s[i];
s[i] = s[r - 1 - i];
s[r - 1 - i] = temp;
}
}
public static void reverse(char s[])
{
// creating character array of size
// equal to length of string
char[] temp = new char[s.length];
int x = 0;
for (int i = 0; i < s.length; i++) {
if (s[i] >= 'a' && s[i] <= 'z'
|| s[i] >= 'A' && s[i] <= 'Z') {
// storing elements in array
temp[x] = s[i];
x++;
}
}
// reversing the character array
rev(temp, 0, x);
x = 0;
for (int i = 0; i < s.length; i++) {
if (s[i] >= 'a' && s[i] <= 'z'
|| s[i] >= 'A' && s[i] <= 'Z') {
// updating the origional string
s[i] = temp[x];
x++;
}
}
String revStr = new String(s);
System.out.println("reversed string is: " + revStr);
}
// Driver Code
public static void main(String[] args)
{
String str = "Ab,c,de!$";
char[] charArray = str.toCharArray();
reverse(charArray);
}
}
// This code is contributed by Aarti_Rathi
# Python3 program to reverse string without
# affecting it's special character
def rev(s, l, r) :
while l<r :
temp = s[l]
s[l] = s[r]
s[r] = temp
l += 1
r -= 1
# creating character array of size
# equal to length of string
def reverse(s):
temp = ['']*len(s)
x = 0
for i in range(len(s)) :
if s[i] >= 'a' and s[i] <= 'z' or s[i] >= 'A' and s[i] <= 'Z' :
# storing elements in array
temp[x] = s[i]
x += 1
# reversing the character array
rev(temp, 0, x)
lst = list(s)
x = 0
for i in range(len(s)) :
if s[i] >= 'a' and s[i] <= 'z' or s[i] >= 'A' and s[i] <= 'Z' :
# updating the origional string
lst[i] = temp[x]
x += 1
revStr = ""
for i in range(len(s)) :
revStr += lst[i]
print("reverse string is :",revStr);
# Driver Code
if __name__ == "__main__" :
s="Ab,c,de!$"
reverse(s)
# This code is contributed by aditya942003patil
// C# code to illustrate how to reverse an array without
// affecting special characters.
using System;
public class GFG{
public static void rev(char[] s, int l, int r)
{
for (int i = l; i < r / 2; i++) {
char temp = s[i];
s[i] = s[r - 1 - i];
s[r - 1 - i] = temp;
}
}
public static void reverse(char[] s)
{
// creating character array of size
// equal to length of string
char[] temp = new char[s.Length];
int x = 0;
for (int i = 0; i < s.Length; i++) {
if ((s[i] >= 'a' && s[i] <= 'z')
|| (s[i] >= 'A' && s[i] <= 'Z')) {
// storing elements in array
temp[x] = s[i];
x++;
}
}
// reversing the character array
rev(temp,0,x);
x = 0;
for (int i = 0; i < s.Length; i++) {
if (s[i] >= 'a' && s[i] <= 'z'
|| s[i] >= 'A' && s[i] <= 'Z') {
// updating the origional string
s[i] = temp[x];
x++;
}
}
string revStr = new string(s);
Console.WriteLine("reversed string is: " + revStr);
}
// Driver Code
public static void Main(string[] args)
{
string str = "Ab,c,de!$";
char[] charArray = str.ToCharArray();
reverse(charArray);
}
}
// This code is contributed by Srj_27
// Javascript program to reverse string without
// affecting it's special character
function reverse(s)
{
// creating character array of size
// equal to length of string
let temp=new Array(s.length);
let x = 0;
for (let i = 0; i < s.length; i++) {
if (s[i] >= 'a' && s[i] <= 'z'
|| s[i] >= 'A' && s[i] <= 'Z') {
// storing elements in array
temp[x] = s[i];
x++;
}
}
// reversing the character array
//reverse(temp, temp + x);
let str="";
for(let i=x-1; i>=0; i--)
{
str+=temp[i];
}
x = 0;
let ans=""
for (let i = 0; i < s.length; i++) {
if (s[i] >= 'a' && s[i] <= 'z'
|| s[i] >= 'A' && s[i] <= 'Z') {
// updating the original string
ans+= str[x];
x++;
}
else
ans+=s[i];
}
document.write("reversed string is: " + ans);
}
// driver code
let s = "Ab,c,de!$";
// function call
reverse(s);
Outputreversed string is: ed,c,bA!$
Time Complexity: O(N) where N is the length of the string.
Auxiliary Space: O(N) where N is the length of the string.
Efficient Solution:
The time complexity of the above solution is O(n), but it requires extra space, and it does two traversals of an input string.
We can reverse with one traversal and without extra space. Below is the algorithm.
1) Let input string be 'str[]' and length of string be 'n'
2) l = 0, r = n-1
3) While l is smaller than r, do following
a) If str[l] is not an alphabetic character, do l++
b) Else If str[r] is not an alphabetic character, do r--
c) Else swap str[l] and str[r]
Below are implementations of the above algorithm.
C++
// C++ program to reverse a string with special characters
#include <bits/stdc++.h>
using namespace std;
// Returns true if x is an alphabetic character, false
// otherwise
bool isAlphabet(char x)
{
return ((x >= 'A' && x <= 'Z') || (x >= 'a' && x <= 'z'));
}
void reverse(char str[])
{
// Initialize left and right pointers
int r = strlen(str) - 1, l = 0;
// Traverse string from both ends until 'l' and 'r'
while (l < r) {
// Ignore special characters
if (!isAlphabet(str[l]))
l++;
else if (!isAlphabet(str[r]))
r--;
else // Both str[l] and str[r] are not special
{
swap(str[l], str[r]);
l++;
r--;
}
}
}
// Driver code
int main()
{
char str[] = "a!!!b.c.d,e'f,ghi";
cout << "Input string: " << str << endl;
reverse(str);
cout << "Output string: " << str << endl;
return 0;
}
// This code is contributed by Sania Kumari Gupta
// C program to reverse a string with special characters
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
// Returns true if x is an alphabetic character, false
// otherwise
bool isAlphabet(char x)
{
return ((x >= 'A' && x <= 'Z') || (x >= 'a' && x <= 'z'));
}
void reverse(char str[])
{
// Initialize left and right pointers
int r = strlen(str) - 1, l = 0;
// Traverse string from both ends until 'l' and 'r'
while (l < r) {
// Ignore special characters
if (!isAlphabet(str[l]))
l++;
else if (!isAlphabet(str[r]))
r--;
// Both str[l] and str[r] are not special
else {
char temp = str[l];
str[l] = str[r];
str[r] = temp;
// swap(str[l], str[r]);
l++;
r--;
}
}
}
// Driver code
int main()
{
char str[] = "a!!!b.c.d,e'f,ghi";
printf("Input string: %s\n", str);
reverse(str);
printf("Output string: %s\n", str);
return 0;
}
// This code is contributed by Sania Kumari Gupta
// Java code to illustrate how to reverse an array without
// affecting special characters.
import java.io.*;
class GFG {
public static void reverse(char str[])
{
// Initialize left and right pointers
int r = str.length - 1, l = 0;
// Traverse string from both ends until 'l' and 'r'
while (l < r) {
// Ignore special characters
if (!Character.isAlphabetic(str[l]))
l++;
else if (!Character.isAlphabetic(str[r]))
r--;
// Both str[l] and str[r] are not spacial
else {
char tmp = str[l];
str[l] = str[r];
str[r] = tmp;
l++;
r--;
}
}
}
// Driver Code
public static void main(String[] args)
{
String str = "a!!!b.c.d,e'f,ghi";
char[] charArray = str.toCharArray();
System.out.println("Input string: " + str);
reverse(charArray);
String revStr = new String(charArray);
System.out.println("Output string: " + revStr);
}
}
// This code is contributed by Sania Kumari Gupta
def reverseString(text):
index = -1
# Loop from last index until half of the index
for i in range(len(text)-1, int(len(text)/2), -1):
# match character is alphabet or not
if text[i].isalpha():
temp = text[i]
while True:
index += 1
if text[index].isalpha():
text[i] = text[index]
text[index] = temp
break
return text
# Driver code
string = "a!!!b.c.d,e'f,ghi"
print ("Input string: ", string)
string = reverseString(list(string))
print ("Output string: ", "".join(string))
# This code is contributed by shiva9610
// C# code to illustrate how to reverse
// an array without affecting special characters.
using System;
public class GFG
{
public static void reverse(char []str)
{
// Initialize left and right pointers
int r = str.Length - 1, l = 0;
// Traverse string from both ends until
// 'l' and 'r'
while (l < r)
{
// Ignore special characters
if (!char.IsLetter(str[l]))
l++;
else if(!char.IsLetter(str[r]))
r--;
// Both str[l] and str[r] are not spacial
else
{
char tmp = str[l];
str[l] = str[r];
str[r] = tmp;
l++;
r--;
}
}
}
// Driver Code
public static void Main()
{
String str = "a!!!b.c.d,e'f,ghi";
char[] charArray = str.ToCharArray();
Console.WriteLine("Input string: " + str);
reverse(charArray);
String revStr = new String(charArray);
Console.WriteLine("Output string: " + revStr);
}
}
// This code is contributed by PrinciRaj1992
<script>
// JavaScript program to reverse a string
// with special characters
// Returns true if x is an alphabetic
// character, false otherwise
function isAlphabet( x)
{
return ( (x >= 'A' && x <= 'Z') ||
(x >= 'a' && x <= 'z') );
}
function swap(str,a,b)
{
var c="";
for(var i=0;i<str.length;i++)
{
if(i==a)
c= c+ str[b];
else
if(i==b)
c=c+str[a];
else
c=c+str[i];
}
return c;
}
function reverse( str)
{
// Initialize left and right pointers
var r = str.length - 1, l = 0;
// Traverse string from both ends until
// 'l' and 'r'
while (l < r)
{
// Ignore special characters
if (!isAlphabet(str[l]))
l++;
else if(!isAlphabet(str[r]))
r--;
else // Both str[l] and str[r] are not spacial
{
str=swap(str,l, r);
l++;
r--;
}
}
document.write("Output string: "+ str +"<br>");
}
var str= "a!!!b.c.d,e'f,ghi";
document.write( "Input string: " + str +"<br>");
reverse(str);
</script>
OutputInput string: a!!!b.c.d,e'f,ghi
Output string: i!!!h.g.f,e'd,cba
Time Complexity: O(N) where N is the length of the string.
Auxiliary Space: O(1).
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